1. Field of the Invention
The present invention relates to a wafer used for evaluation of uniformity of furnace temperature, gas concentration and the like, removal of polluting materials, determination of various conditions, and the like, in production of silicon wafers (hereinafter, referred to as xe2x80x9cdummy waferxe2x80x9d in some cases), and a method of producing the same.
2. Description of the Related Art
In a process of producing a semiconductor such as LSI and the like, a process of oxidizing the surface of a wafer, a process of diffusing doping elements such as phosphorus, boron and the like in wafer, a process of forming various films on the surface of a wafer by CVD (chemical vapor deposit) or PVD (physical vapor deposit) and the like are important, and the way of keeping treatment conditions in these processes constant is important in improving the yield of an article and producing a more highly-integrated device. In general, in these processes, a boat charged with 100 or more wafers is placed in a treating furnace and subjected to a batch treatment.
In the batch treatment, however, there are problems such as generation of a difference in temperature in the above-mentioned treating furnace, a difference in temperature of a raw material gas, and the like. Therefore, the difference in temperature in the above-mentioned treatment furnace, difference in temperature of a raw material gas, and the like are tried to be solved by placing a dummy wafer not used as a product wafer, at positions revealing a fear of differences of conditions such as temperature in the above-mentioned treating furnace, temperature of a raw material gas, and the like from given conditions, and analyzing whether the thickness, components and the like of a thin film formed in the dummy wafer are the same as in the case of a wafer placed under given conditions, or not. Further, this dummy wafer is used also for the purpose of investigating conditions for a plasma treatment in an etching treatment apparatus and removing particles generated in the apparatus.
Such a dummy wafer is generally used at high temperatures repeatedly, and treated with an acid repeatedly for periodic use by removing films formed thereon. Conventionally, as the material of this dummy wafer, the same silicon, quartz and the like have been used as in the case of materials of usual product wafers. However, in the case of a dummy wafer formed of silicon, since heat resistance is not so good, the form tends to change by time and acid resistance is not sufficient, therefore, the surface thereof is roughened owing to solution, particles are liable to be formed, and the life is short. On the other hand, in the case of a dummy wafer formed of quartz, heat resistance and acid resistance is not sufficient, and an etching treatment and the like cannot be effected due to no-conductivity. Accordingly, carbon materials excellent in heat resistance and ceramics materials excellent in acid resistance are expected as the material of a dummy wafer instead of silicon and quartz, and of them, a sintered silicon carbide is most highly expected since constituent elements thereof manifest no problems on the semiconductor device product.
However, since silicon carbide is a material, which is not easily sintered, it has been usual to add small amount of boron carbide, alumina and the like as aids for the sintering. Because these aids are impurities for a dummy wafer, methods of producing a sintered silicon carbide are recently provided. For example, there are i) a method in which a fine particle is formed by gas phase growth and the formed powder is used as a raw material to produce a sintered body, ii) a method in which a sintered body in the form of plate is directly produced by gas phase growth, and the like, using as a raw material a gas and solution containing silicon and carbon.
A wafer made of a sintered silicon carbide obtained by these methods is generally produced by a method in which a sintered silicon carbide obtained by molding a silicon carbide powder by a hot press method and the like is sliced by discharge processing and the like, then, chamfer, washing, drying, polishing and the like are effected. Since thus obtained wafer has a problem of a tendency of crack generation, a solution thereof is desired and particularly, it is desired that crack does not occur in imparting thermal shock.
An object of the present invention is to provide a high quality wafer which improves thermal shock resistance, causes no generation of crack by thermal shock, and suitably used for evaluation of uniformity of furnace temperature, gas concentration and the like, removal of polluting materials, determination of various conditions, and the like, in production of silicon wafers (dummy wafer), and a method capable of producing this wafer efficiently.
In the first aspect of the present invention, this invention provides a method of producing a wafer comprising:preparing a sintered silicon carbide cut in the form of wafer;and subjecting the sintered silicon carbide to a baking treatment. In another word, this invention provides a method of producing a wafer comprising: preparing a wafer which is obtained by cutting a sintered silicon carbide; and subjecting the wafer to a baking treatment to reduce process residual stress.
In the second aspect of the present invention, this invention provides a wafer produced by the above-mentioned method.
In the method of producing a wafer of the present invention, a baking treatment is effected on a sintered silicon carbide cut in the form of wafer. By this baking treatment, process residual stress accumulated before the above-mentioned baking treatment in the above-mentioned sintered silicon carbide is removed. By this, in the resulted wafer, generation of crack in receiving thermal shock is effectively suppressed.
In the wafer of the present invention, stress imparted in processing does not remain and generation of crack in receiving thermal shock is effectively suppressed, since this wafer is produced by the above-mentioned method of producing a wafer of the present invention.